Radio Caroline 648 kHz power increase on November 25 2021

Below is a plot of the signal strength of Radio Caroline's 648 kHz signal as received in Enschede, the Netherlands in November/December 2021. Vertical axis is relative power in dB; carrier power has been averaged over 1-second intervals and plotted as dots. Horizontal axis is UTC date.

The increase in power is clearly visible when looking only at the daytime measurements. During daytime there's only groundwave propagation, resulting in quite a stable signal, fluctuating only one dB or so. At night, skywave propagation makes the signal stronger but also highly variable due to fading; furthermore, there may also be interference from other stations on the same frequency.

Looking more precisely, by taking the median of signal strength between 10:00 and 13:00 UTC and comparing that before and after November 25, the increase is found to be 6.2 dB, which is equivalent to a power increase by a factor of 4.2. Officially, they went from 1 to 4 kW, a factor of 4.0 rather than 4.2. But I guess no one really cares about that difference ;-)

On November 24, already a small power increase is visible. A Radio Caroline engineer reading this page told me that they in fact switched to the new transmitter on this day, but ran it at low power overnight. Zooming in, we can even see exactly when the switch-over happened: